The struggle for existence is a driving factor of evolution, a set of relationships between animal and flora between themselves and with the outside world. Scientist Charles Darwin identified three forms of struggle for existence:
- The relationship of organisms with inanimate nature, or adaptation to abiotic factors external environment;
- interspecific struggle, which includes the relationship between individuals belonging to different species;
- intraspecific struggle, including the relationship between individuals of the same species.
Form 1. The relationship of organisms with inanimate nature
The relationship of organisms with inanimate nature can be shown in the following examples.
Plants of the North are more frost-resistant than southern forms, because specimens that cannot bear low temperatures, died out and the offspring survived only from those of them that, as a result of mutational variability, acquired frost resistance. The herbaceous vegetation of the tundra has a short growing season, which allows the formation of seeds during a short summer. And this is a consequence of the fact that plants that did not have time to form seeds for short term northern summer, could not leave offspring. And here, in the struggle of life, those who, due to the corresponding hereditary changes, had a shortened growing season, won.
Drought adaptation
An even shorter growing season for the herbaceous vegetation of deserts, which ensures their maturation in a few days of the wet spring period.
Imagine a picture from the past ... A plant with a relatively long growing season lived at the edge of the desert. Its seeds were blown towards the desert. They undoubtedly had individual differences, which manifested themselves in the speed of emergence of seedlings, the intensity of growth and maturation, so not all of them could survive and leave offspring.
Some individual characteristics turned out to be appropriate for the conditions of existence, however, they also gave seeds that were also not of the same type. Again, selection retained only those plants that were most adapted to the specific conditions of existence. Moreover, the seeds of these plants fell even further into the depths of the desert. Among the plants that grew from these seeds, selection was again made for the ability to survive in an even shorter growing season. This is how plant species with a short growing season (ephemera) were formed in nature.
In other plants - desert dwellers - selection went in other directions, which ensured the emergence of new traits that made it possible to exist in these conditions. Native to deserts Central Asia saxaul has no true leaves. They have developed into pointed scales pressed against the stem, or even small tubercles on the stem, which prevents abundant evaporation of water. Thus, this feature is also a consequence of selection, i.e. the survival of those who lost less moisture.
It is possible that a mutation of plants with reduced leaves did not appear immediately, but the reduction of the evaporating surface in plants - the ancestors of saxaul - went through a series of stages (mutations). The selection kept those who survived better, they turned out to be plants that evaporated less moisture.
An interesting example is given by Darwin regarding insects - inhabitants of small oceanic islands. They either fly beautifully, or are completely devoid of wings. Apparently, carried by sudden gusts of wind were carried away into the sea, only those that could withstand the wind, or did not fly at all, remained. Selection in this direction led to the fact that on the island of Madeira, out of 550 species of beetles, 200 species are flightless.
Form 2. Interspecies struggle
As a result interspecies struggle there were those adaptations that are necessary for plants and animals in their complex relationships with each other. So, the plants got thorns, thorns, stinging hairs, a bitter taste, etc.
You can imagine that ancient ancestor rosehip thorns were absent. The leaves and branches on the bushes of these plants were eaten by herbivores. But on some bushes, the stems had a slight roughness. Such bushes were less willing to overeat. In the end, those survived, in which the thorns became larger and larger. Exactly the same process led in some cases to the formation of thorns, in others to the appearance bad smell or taste and miscellaneous eating characteristics.
Among plants pollinated by insects more seeds could form those that better "attracted" pollinating insects. Bright color, aroma, abundant sweet nectar, flower structure, etc. played a role here. As a result, those of the varieties that were inferior to others in this respect, ceased to be visited by insects and, in the end, were doomed to extinction.
The origin of the color of animals
Insects, lizards and a number of other species hiding between the leaves of plants are green or brown in color, desert dwellers are the color of sand. The color of animals living in forests, for example, a leopard, has spots that resemble glare, while in a tiger it imitates the color and shadow of the stems of reeds or reeds. This color is called patronizing.
In predators, it became entrenched due to the fact that its owners could quietly sneak up on prey, and in organisms that are prey, a protective coloration is a consequence of the fact that the prey remained less noticeable to predators. How did it come about?
Camouflage helps hide from predators. If you could not find it, scroll to the next picture
Numerous mutations have given and give big variety forms that differ in color. In some cases, it turned out to be close to the background of the environment, i.e. hid the animal, played a protective role. Those animals in which the protective coloration is weakly expressed, either remained without food, or themselves became victims.
Sometimes animals, not only in color, but also in shape, are similar to any objects or other animals. This phenomenon is called mimicry. The moth caterpillar frozen on a tree branch is almost indistinguishable from a knot.
Symbiosis between species
The interspecific struggle reached particular intensity at various stages of evolution in cases when the improvement of one group of organisms necessitated the improvement of another, dependent group:
These are examples of the so-called conjugate evolution, which is a very important form of development, as it leads to long-term mutual improvement of many groups of animals and plants.
Form 3. Intraspecific struggle
The intraspecific struggle for existence is the most intense, has a complex and most acute character, because individuals and populations of the same species need the same conditions for the existence and abandonment of offspring.
Intraspecific struggle can be for the female, for leadership in the flock, for more profitable habitats Of the animals belonging to one species and serving as food for a certain type of predators, the less adapted, for example, those with the least protective coloring, slower running, etc., become prey in the first place. The same is observed in predators. The more successful prey goes to the more adapted: more dexterous, faster, savvy, etc.
The more adapted not only have an advantage in their own survival, but also in providing their offspring with food, and, consequently, in its survival. It can be seen from the examples given that, for example, butterflies, hares, foxes belonging to the same population do not directly enter into a struggle with each other, but indirectly between them there is a rivalry for the right to survive and at the cost of the death of less adapted fellows the more adapted survive.
Fighting between individuals and herd instinct
But in a number of cases, a direct competition takes place between individuals of the same population. In some animal species, there is a rivalry between males of the same population because of the female (many species of spiders, capercaillie, black grouse, turukhtans, deer, elk). The stronger ones win the victory. Intraspecific struggle should also include the division of the habitat into " hunting grounds", Which are defined in songbirds by the voice, in mammals, most often by odorous secretions, etc.
Excessive increases in populations can cause food shortages. In such cases, fertility decreases in a number of species (for example, murine rodents). Some birds (tits, storks, cranes, cranes) kill part of the offspring, usually sick and weak chicks. Excessive growth in population numbers leads to outbreaks of epidemics that reduce the number of populations. But even the most adapted survive, for example, those who have an innate immunity to these diseases.
Some animal species have developed an adaptation to live in herds (deer and many other ungulates) or colonies (seagulls), which provides better protection from predators. Predators can unite for a common hunt (wolves).
| comparison table forms of struggle for existence (with examples) | |
|---|---|
| Form | Description |
| Fighting the environment | Unique properties that allow you to survive in conditions unfavorable environment(droughts, frosts, aggressive environments) give advantages to the organism of one species over others. Example: animals change color in winter, hibernate; exterminated plants have high seed productivity, vegetative reproduction is characteristic. |
| Interspecies struggle | The struggle for survival between species located in the same territory and claiming the same resources. For example: plant thorns (rose hips), an unpleasant / poisonous taste or smell allowed for longer survival and longer offspring compared to other species. Gray rats have supplanted black rats, being more aggressive and better swimmers. |
| Among the individuals of one species, the least adapted individuals were the first to go to food for predators. Weaker individuals of predators find it more difficult to get food, and therefore feed the offspring. For example: among antelopes, only healthy and strong individuals survive, the rest go for food. Among coniferous forest the same age, some trees grow more, the roots go deeper, suppressing weaker trees. | |
It should be emphasized that all forms of the struggle for existence are closely intertwined. If there is no doubt that the streamlined shape of the fish's body is due to living in water, then this shape was formed not as a result of the action of the water itself, but as a result of competitive struggle with other animals of their own and other species. For some, it provided an opportunity to overtake prey, for others - to escape from the enemy.
The study of the struggle for existence, intraspecific and interspecific relations is of great practical significance to develop measures to combat pests in agriculture and forestry, when breeding useful species, for fisheries and hunting, etc. It is enough to recall the variety of forms of biotic connections, and the role of their study in the rational human activity in ecological systems becomes clear.
struggle for existence
in biology - one of the basic concepts in the theory of evolution by Charles Darwin, which he used to designate the relationship between organisms, as well as between organisms and abiotic conditions, leading to the death of the less adapted and the survival of the most adapted individuals, i.e. to natural selection. The complexity of the problem and the metaphorical nature of the term gave rise to it different interpretations and even the elimination of this concept from evolutionary biology by some modern Darwinists. Attempts were made to transfer the doctrine of the struggle for existence to human society (social Darwinism).
Struggle for existence
(biol.), metaphorical expression proposed by Charles Darwin (1859) to determine the activity of the organism, aimed at preserving life and ensuring the existence of offspring. B.'s concept for p. closely related to natural selection. In the very general view B. for s. arises from the discrepancy between the high ability of organisms to reproduce and the limiting dimensions of space, food reserves, water, etc., necessary for the normal existence of organisms of any kind. So, according to Darwin's calculations, provided that all the cubs born to the world survived and reproduce, a pair of elephants - one of the slowest breeding mammals - would leave 19 million offspring in 750 years. One diatom with unhindered reproduction, it could cover the entire surface of the Earth with a film within a day and a half. However, this potential ability to reproduce is never fully realized in nature. Most of emerging individuals do not live up to adulthood and dies in the process of direct or indirect B. for s. ≈ either under the influence of unfavorable climatic and other abiotic factors of the environment (constitutional biology for the village), or in the struggle against representatives of other species (interspecific biology for the village), or in the struggle against individuals of its own species (intraspecific biology for the village. ). Constitutional and interspecific B. for s. in themselves are only annihilating factors. Only intraspecific struggle leads to the creation of new forms of organization. When describing the processes of intraspecific B. for s. often use the concept of competition. The result of the competition of dissimilar individuals of a given species in the struggle for life and reproduction is selective elimination (destruction); general elimination, or accidental extermination, individual elimination (including direct elimination by physical factors, biological factors and indirect elimination by physiological factors; the latter is reduced to the experience of less depleted individuals), family elimination and group elimination. In evolution special meaning has a mix of individual and group elimination. Elimination takes on a selective character only through competition, which can be intragroup (individual active and passive), interfamilial and intergroup (I.I.Shmalgauzen).
Intraspecific B. for s. manifests itself in competition between individuals of this species when they collide with any enemies and harmful influences, in competition when using food and other vital factors (light, water, etc.) and in competition in means of more effective protection of life and offspring. Interspecific B. for s. can flow directly between a predator and a prey, as well as between individuals of different, sometimes very distant species: herbivorous mammals and herbivorous insects (for example, locusts, grasshoppers) compete, “fight” for food.
In B.'s concept for s. includes, according to Darwin's definition, all forms of relationships between organisms, and not only competitive relationship struggle in the narrow sense of the word. Since the time of Darwin, the greater importance of biotic conditions (i.e., the vital activity of other creatures with whom given organism associated with food and any other relationship) than abiotic.
Vulgarizing interpretation of B. for s. in nature and arbitrarily transferring its laws to public life, some bourgeois sociologists and economists put forward the concept of social Darwinism, which was sharply criticized by F. Engels (see Anti-Dühring, 1966, pp. 64-66). The methodological error of the social Darwinists consists in an attempt to reduce social laws to the level of biological ones. Having shown, following B. Franklin and K. Linnaeus, the existence in nature of the desire to reproduce in geometric progression, Darwin actually refuted the main idea of the English economist T.R. Malthus (see Malthusianism) about the alleged discrepancy between human reproduction (exponentially) and arithmetic progression), to which K. Marx specially drew attention (see K. Marx and F. Engels, Soch., 2nd ed., vol. 26, part 2, p. 127).
The concept of B. for s., Put forward by Darwin, had critical importance, reflecting at the level of natural science in the 19th century. internal driving force evolution and serving Darwin as one of the most important initial premises in the creation of the theory of development organic world... Comparing the presence of B. in nature for s. with the observed diversity of individuals within any species, Darwin came to the conclusion that natural selection is the main driving factor evolutionary process... Thus, the doctrine of evolution was placed on a materialistic natural-historical basis. Remaining a broad generalizing concept, B. for p. in a specific study, it breaks down into a number of phenomena associated with the study of biogeocenotic relations at the level of populations, species, biocenoses, relationships between organisms and abiotic factors environment, etc. In all cases B. for s. leads to comparative assessment individuals of a certain population in a specific biogeocenosis, to selective elimination and natural selection.
Lit .: Darwin C., The Origin of Species by natural selection or the preservation of favored breeds in the struggle for life. Works, vol. 3, Moscow-Leningrad, 1939; Shmalgauzen I.I., Problems of Darwinism, M., 1946; History of evolutionary doctrines in biology, Moscow-Leningrad, 1966.
A. V. Yablokov.
Wikipedia
Struggle for existence
Struggle for existence- one of the driving factors of evolution, along with natural selection and hereditary variability, a set of diverse and complex relationships that exist between organisms and environmental conditions. Also, the third chapter of Charles Darwin's book "The Origin of Species by Natural Selection" has the title "The Struggle for Existence."
- The essence of the struggle for existence
- Subdivision of it
- Struggle with the external environment
- Intraspecific struggle for existence
- Struggle among plants
- Fighting among herbivorous and carnivorous animals
- Interspecies struggle for existence
- Its dependence on the mobility of animals
- The emergence of struggle with the invasion of new animals
- Conclusion
The concept " struggle for existence"Was first introduced into the science of life by Charles Darwin, who in Chapter III of his book" The Origin of Species "showed the spread of the struggle for existence in animals and plant kingdom and clarified great value this phenomenon.
Main and the main reason struggle for existence Darwin considers excessive reproduction inherent in all animals and plants. In fact, all living things give rise to significantly more offspring than can feed in a given area under existing conditions. If we imagine, for example, that all the hundreds of thousands of seeds produced by one single birch would sprout in the area where the wind could bring them, and would give adult trees, then, undoubtedly, very soon a dense forest and a birch would form around this tree would crowd out all other plants. This is not the case only because of the multitude of seeds, only very few find themselves in such favorable conditions that they can germinate, and of the number of germinated plants, even fewer manage to reach the size of an adult tree. Most are young. sprouts are drowned out by other plants, eaten by animals, dies from lack of light, water and nutrition. Likewise, among animals, many are of absolutely exceptional fertility. Especially in this respect, some fish are remarkable, for example, the number of eggs spawned by cod reaches 10 million, sea burbot spits up to 60 million, and lund-fish even up to 3000 million eggs, and, nevertheless, the number of these fish in the seas does not increase in any noticeable size. It is clear that of the many millions of fry emerging from eggs, only a few reach maturity, while the rest die in the struggle for existence - they are eaten by predators or perish from unfavorable external conditions.
However, even with a low degree of fertility, but over a long period of time, the number of offspring can turn out to be very significant, - so, according to Darwin, “an elephant is revered as an animal that reproduces the slowest of all, - we will be left behind the truth if we accept that it reproduces from thirty to ninety years of age and during this period of time produces three pairs of cubs, but if so, then in 500 years the offspring of one pair of elephants would have consisted of 15 million individuals. " Likewise, a condor, for example, lays only a couple of eggs, and a petrel only lays one egg, and yet these birds could produce huge offspring.
The abundance of offspring in animals could lead to a strong overpopulation of each of the areas in which they live. This desire for overpopulation leads to a struggle for existence, as a result of which a mobile balance is established over the centuries between the number of individuals of certain species of plants and animals. At the same time, numerical ratios fluctuate within certain limits, but do not go beyond these limits.
The concept of the struggle for existence was somewhat refined and systematized by later research. In it, first of all, it is necessary to distinguish between the struggle of a living being with the conditions of the inanimate external environment from the struggle with other living organisms. In the first case, we do not even have, properly speaking, a "struggle" in the real sense of the word; a living organism, with all its structure and mode of action, only resists those conditions of the external environment that are disastrous for it, it develops various protective devices, modifies his instincts and habits to defend his existence. If, however, the measures of protection taken by him are not enough, he dies under the influence of not favorable conditions... In this case, death, depending on the circumstances, can be individual (captures only one individual), group, or, finally, mass, caused by catastrophic disasters, such as floods, the onset of sudden frosts, etc. In the same way, a catastrophic change in external conditions can be either sudden and short-term, or gradual and long-term, such as climate change, desalination or salinization of water bodies, their drying, etc. In all cases of mass extermination of living beings by forces inanimate nature both well-adapted and poorly adapted individuals perish equally, and here there is no need to talk about the survival of the fittest. With the death of an individual, occurring under the influence of unfavorable external conditions, on the contrary, cases are possible when individuals who are less adapted to these conditions will die, and the most adapted will survive.
We can talk about a real struggle for existence only if the matter: concerns the mutual relations of living beings, between which there is either a direct struggle, or competition on the basis of obtaining food, light, warmth and other vital benefits. Moreover, such a struggle can be intraspecific- between individuals of the same species, or interspecific- between living beings belonging to two different species.
Questions related to mass or single death under the influence of external conditions can be left without detailed consideration here, since they do not relate to our topic (the relationship of living beings).
Intraspecific struggle for existence is primarily due to the overproduction of offspring by animals and plants that do not correspond to the possibilities of existence. The space around every living organism is already inhabited by other organisms, and many of them need the same food and in the same conditions of existence as the given organism. The offspring that is born finds for itself only a little free space and great amount Competitors, already strong and well adapted to these conditions, while he still needs to grow and adapt to these conditions. It is clear that at the very beginning there is a huge death of the offspring, and if it were few in number, then the probability of survival of individual individuals would be very small.
Overproduction of offspring is nothing more than an adaptation that increases the likelihood of survival of young individuals.
In the nature around us, the conditions of the intraspecific struggle for existence are very complex. The struggle between individuals of the same species in plants is most vividly reflected - they are not capable of actively changing places and, at the same time, have enormous fertility, causing overpopulation. The latter gives rise to intense competition between individuals, leading to the death of most of them. Every forest provides ample proof of this if you examine it carefully. Studying trees, their height, thickness and features of the development of their crown, you can always notice that there are a certain number of trees, the crowns of which rise high above the general canopy of the forest, the vast majority of trees form this canopy, and, finally, many trees do not reach the height of the general canopy and hiding under it. Among the latter, there are those that are only slightly below the general canopy, and, on the other hand, there are very low trees with a poorly developed crown. One would think that these are trees of different ages, but in fact the same is observed in the forest of the same age.
This distribution of trees in the forest is well known to foresters and botanists. Foresters divide all trees in the forest into five classes according to their development. The first class includes trees that are exclusively dominant, forming the canopy of the forest, the third class includes trees that are slightly below the canopy and with poorly developed crowns - these are candidates for oppression - and the last two classes are trees that are muffled and completely oppressed. The reasons for this difference in the development of trees of the same age lie solely in intense competition due to the nutrition extracted from the soil (salts, especially those containing nitrogen), due to moisture, and especially due to sunlight so important to plant life.
Indeed, if we consider a felling or some area covered with young spruce shoots, then one can count hundreds of thousands of young trees per hectare, while in an adult, 100-150-year-old forest there will never be more than several hundred trees per hectare. It is already clear from this that hundreds of thousands of trees could not withstand the competition and died in the struggle for existence, drowned out by their happy brothers. While the trees were small and grew more or less far from one another, there was enough space, moisture and light for them, but as they grew, they began to shade each other, and those who accidentally climbed higher took away light from those below. At the same time root systems they collided, intertwined, and the stronger overgrown roots took away water and food from the weaker ones.
With further growth, the crowns of the trees that had overtaken in growth also closed, and took away space and, most importantly, light from those below. In such a competition for light, food and place, the weakest specimens of trees were soon defeated. Growth retardation was the most influential factor here; those trees that for some reason began to lag behind in height, very quickly covered with crowns of others, growing faster, and passed into the class of oppressed, and then completely wither and died from lack of nutrition, moisture and light.
A different degree of seedling development already at the very beginning often determines the further fate of the trees. Those trees that have just emerged from the seeds, which have managed to develop faster and overtake their comrades, receive significant advantages in the further competition. The heterogeneity of the soil, sometimes more nutritious, sometimes leaner, also imposes its stamp on the tree and accelerates or retards its growth. Foresters have long ago received figures that clearly express the results of this struggle for existence among the forest trees. So, for spruce forest growing freely without any human intervention, G.F. Morozov gives the following data on the number of trees per hectare.
The data show that the most acute struggle for existence and the greatest death of unlucky trees occurs during 60 years, when the crowns of trees grow and close; in the second sixty years, the number of trees is reduced by only one third.
Such a sharp picture of death in the struggle for existence is found in plants, of course, primarily due to the fact that they cannot leave the place, cannot escape the unfavorable conditions created by competition, and find more suitable conditions. Representatives of the animal kingdom, with a few exceptions (sedentary animals), have mobility and can settle in search of favorable living conditions. However, this advantage does not save them from the struggle for existence. Their life entirely depends on food, which is scattered in space and must be found and obtained by them. The amount of food in a particular area is due different reasons and may not correspond at all to the needs of the number of individuals that were born, the possibility of finding other areas richer in food depends entirely on the means and methods of movement, on existing natural obstacles, and finally, on the distances that have to be overcome.
It is quite natural that under these circumstances the struggle for existence in animals proceeds in even more complex forms than in plants, and it is more difficult to notice it. That it should happen is already said by those huge size fertility inherent in some fish, which we talked about above. True, of the millions of fry that emerged from the eggs of a cod or moon-fish, a significant part die from unfavorable external conditions or are eaten by predators (which refers to the field of interspecific struggle for existence), but there is no doubt that some of them also die due to lack of food or even simply devoured by its more rapidly developing cousins.
The intraspecific struggle for existence is also clearly revealed during the mass reproduction of such herbivorous animals as mice, ground squirrels, locusts and other field pests. Their mass reproduction usually occurs due to the fact that, due to some particularly favorable external conditions, the offspring of a given species of animals, born in a year, survive to a greater extent than usual, and the next year or in the same year appears in an extreme set. In this case, all the food suitable for this species is usually eaten in the immediate vicinity and, under the pressure of hunger, the animals sometimes gather in huge flocks and set off in search of food. At the same time, they make significant journeys, capturing and devastating large areas, as, for example, the locusts, which are a real disaster, do.
In the end, however, the lack of food causes an intensified struggle for existence, and developing from congestion and crowding infectious diseases decrease in numbers, animals die in masses, and little by little, under the influence of any unfavorable conditions, their previous normal numbers are restored.
Among carnivores, the intraspecific struggle for existence is less obvious, since its conditions are even more complex. The life of carnivores, or predators, depends on the location of prey, often very diverse, and the number and distribution of each species that make up this prey can be subject to different fluctuations in the predator's hunting area and depend on a number of other complex and unstable conditions. It is, of course, unthinkable to take into account all the possibilities and chances of victory and defeat for each individual, but, ultimately, the number of carnivores, no doubt, is still regulated by the number of their victims and fluctuations in the number of the latter, depending on many conditions.
It should be noted that carnivores, with a lack of food, often attack their fellows, especially the weaker ones, and destroy them. So, it is known that in zoological gardens it is possible to keep in one cage only equally strong and large owls, but if between them there is a weak, young or sick, they will tear it to pieces and eat it. When keeping lobsters caught in the sea in cages, fishermen tie their claws to them, as otherwise they attack weaker, recently faded brethren and devour them. With a lack of food, the instinct of preserving offspring, which is so strongly developed in animals, is sometimes drowned out. So, the male stickleback fish, who so carefully builds a nest for caviar and carefully protects it during development, often pounces on them after the fry emerge and devours them. The stomachs of frogs in spring are also sometimes chock-full of tadpoles. Of course, all such cases are an exception. Usually instinct keeps animals from direct attack on their own kind, and especially on their offspring.
Let's move on to consideration interspecies struggle for existence, that is, struggle, or competition, between different species inhabiting; common area and differing from each other more or less significantly in structure and way of life. In this struggle, the success of every living being depends entirely on following conditions: first, on the ability to resist harmful influences external environment - cold, heat, dampness, etc., secondly, from the ability to escape from the pursuit of larger and more powerful enemies and, thirdly, from the ability to obtain the necessary food. In addition, it is important to what extent these abilities can be higher and more perfect than the same properties of other species living in the same area and eating the same food.
The conditions of competition and struggle for existence are very different and depend on the degree of mobility of both the organisms themselves and their prey. If we have before us organisms motionless, for example, several species of various plants competing with each other in a certain area, then, as we have already seen with the example of trees in the forest, the main advantages that give victory in the struggle for existence are the speed of development and growth, and also the abundance and power of the main food organs - roots and leaves. A plant that can quickly develop its stem or trunk, spread its roots wider in the ground, and expel the most abundant and powerful foliage above the surface of the earth, will intercept light and nutrition from other plants, its neighbors, and win over them. Of course, in this case, the adaptability of the plant to the given soil plays an important role. On unsuitable grounds, it lags behind its competitors and is drowned out by them. Fertility is also important, since with a large number of seeds carried by the wind or spread in other ways, there is a greater chance of finding suitable conditions and gaining the upper hand over competitors.
If the competing creatures are themselves mobile, but their life depends on immobile organisms scattered in the surrounding space, then the conditions of the struggle for existence will be different. This fact takes place in competition different types herbivorous animals. The success of one or another competitor in this case depends primarily on the random distribution of food, i.e. plants, in the area where the competitor was born, then on the speed of its movement, since it allows you to move to new areas abounding in food. and also saves from the pursuit of predators. Of course, the perfection of reproduction also plays a role. The latter covers losses caused by predators. Strength and agility usually do not have of great importance for herbivorous animals. In the absence of them powerful weapons active protection they cannot defend their lives in a direct struggle, they are most often saved by their legs. But we often observe in them various organs of passive protection: thorns, shells, shells, protective coloration.
In the struggle for the existence of mobile living creatures that feed on mobile prey (such are all predators), success is based on the most complex and difficult to take into account conjuncture. Their food is scattered in space, mobile and often well protected by passive and active adaptations, so that it is required not only to find it, but also to overtake it, and master it, sometimes in a struggle that is not without danger for the attacker himself. It is clear that predators are required not only to move faster than their prey, but also best development sense organs, as well as agility, energy and strength. Chances in the struggle for existence have a competitor who possesses these qualities to a greater extent than others.
In a wild, untouched by man nature, the struggle for existence between separate types plants and animals, although it is a constant phenomenon, rarely manifests itself in sharply expressed forms. Usually we find in nature some equilibrium that has already been established for centuries and millennia between individual species, and the decline of some and an increase in the number of others occurs within limited limits. Only with any sharp changes in external conditions - with a change in climate, salinization or desalination of water bodies, with a change in soil properties, due to leaching, weathering, etc. - is there an exacerbation of the struggle for existence. This is due to the fact that for some species conditions become more favorable than for others, and the former crowd out rivals who are less adapted to new conditions. In these cases, we can sometimes observe a complete change in everything. natural landscape: so, when the swamps dry up, they can be replaced by forests, and forests, with climate change, can disappear and give way to the advancing steppe, finally, if the steppe is covered with sand or salinized, it can turn before our very eyes into a sandy or saline desert. At the same time, some plants are replaced and displaced by others - the winners in the given conditions in the struggle for existence.
Following the plants, changes and animal world, moreover, in it, too, new winners are found, ousting the vanquished.
In some cases, we find among animals the manifestation of a kind of more active struggle. So, in Europe, there are currently two types of rats: black and gray, also called pasyuk. Pasyuk, as an animal stronger, larger and more agile, drives out the black rat everywhere. At present, the black rat has become a rarity and is found in large numbers only where the pasyuk has not yet managed to penetrate. Meanwhile, according to literary data, before the black rat dominated in Europe, and the Pasyuk was not known (about this, however, experts now have some doubts). According to Pallas, Pasyuk invaded Europe from the east in 1727, as if after an earthquake in Caspian countries... It was observed that a large number of gray rats swam across the Volga at Astrakhan, and then from there they began to settle to the west. At the same time, in 1732, the Pasyuk was brought by ships from the East Indies to England and from there began to settle across Europe from the other end, in the direction to the east. IN East Prussia it appeared in 1750 and by 1780 had settled throughout Germany. In 1753, he first appeared in Paris and in 1809 became famous in Switzerland. In 1775 he was brought to North America, and there, without meeting any competition, it spread rather quickly.
Thus, there is reason to believe that this rat, which came from the east, in a very short period conquered Europe and America and at the same time most actively defeated her rival - the black rat.
Such examples are known among some invertebrates. So, the long-legged Volga crayfish, previously common only in the rivers flowing into the Caspian, Black and Azov sea, after digging the channels connecting southern rivers with the northern ones, moved to the rivers of the Baltic basin and Of the White Seas and, having met here our northern wide-legged crayfish, which has shorter claws, began to gradually displace it, apparently due to its greater adaptability to catching prey and to defend against attack. In places in northern rivers wide-legged cancer has become a rarity.
There are especially numerous examples of such a rapid spread in foreign countries of animals brought in by man from afar, accidentally or deliberately.
These examples testify at the same time to the fierce struggle for existence that arises between the aliens and representatives of the local fauna, for which they are often dangerous competitors. So, the European sparrow, brought to North America, spreading very quickly there, completely supplanted the American finch. Everyone also knows what a true disaster the rabbits brought there have become in Australia; huge sums had to be spent annually on their extermination, and yet they could not be dealt with. They were, on the other hand, very dangerous competitors for the native herbivorous marsupials.
Examples of such a struggle for existence are known even among lowly organized beings.
For example, in Argentina, Chile and Australia, local earthworms were completely supplanted European species accidentally brought there along with the plants.
In all such cases, the displacement of local forms and their defeat in the struggle for existence occurs, of course, because usually the most widespread and, therefore, the most hardy and prolific species are brought into another country. In their new homeland, they do not meet those enemies, the struggle with which prevented their excessive reproduction in their former homeland. If they do not meet serious competitors, if the environmental conditions for them are acceptable and there is enough food, their rapid reproduction begins and the displacement of local animals.
All examples of strong reproduction of imported animals and plants show quite convincingly how great the importance of the natural balance that is established in a certain area as a result of centuries of struggle for existence and competition between native species of animals and plants. Obviously, the fertility of living things and the number of offspring they produce per year is established in strict accordance with both external conditions environment, and with the need to replenish the loss that is natural enemies and competitors. It inevitably also depends on the average amount of food in a given area of residence.As a result, the population size fluctuates from year to year about a certain average, as it fluctuates around average values in normal conditions and all of the above factors. The appearance of new aliens invading the area, upsets the sharply established balance and can create an extremely unfavourable conditions for the former population; to reduce its food supply, to deprive it of habitable places, or, in the case of plants, to take away light, moisture and nutrition.
Therefore, we see that in this case, living beings treat their living environment in exactly the same way as they treat the inanimate. environment: if the living beings surrounding each given organism are useful for it, contribute to its well-being, serve it as food or for any other purposes, then they are used by this organism, since it comes into contact with them. If, on the contrary, they hinder him life goals, taking away from him the means of subsistence, this organism, to the extent of its strength and capabilities, eliminates them, entering into struggle or competition with them, in a word, he treats them like any natural obstacle.
Generally speaking, live environment is for every living organism no more than an environment with which it has to reckon, regardless of whether it consists of representatives of other species, of its own relatives, or even of its own offspring.
1) Many insects are harmful. There is a fierce struggle for existence between insects, plants and insect enemies. Explain why notdestroy insects, because now there are effective means? 2) Why is the author of the book "In the world of insects" D.V. Panfilov says continents are dead without insects?
3) Cod fry often settle under the bell jellyfish, whose tentacles are poisonous. What form of struggle for existence in question?
4) Experiments with sowing mustard showed that under conditions of extreme thickening (the seeds literally touched each other), the death of plants was about 85%, when seeds were sown much less often - 65% died. At the minimum density (2 cm ^ 2 per seed), seedling mortality was 7 - 17%. What provisions evolutionary teaching can the observed phenomena be explained?
1. What is the action of natural selection? 2. Is it possible to obtain experimental confirmation of the effect of selection? 3. What leads to the struggle forExistence? 4. What forms of struggle for existence do you know?
1. Find the name of the species criterion in the specified list 1) cytological 2) hybridological 3) genetic 4) population 2. The scientist who introduced
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